CN115815882A

CN115815882A - Solvent-free rosin-free soldering flux for micro-bump welding and preparation and soldering assisting methods thereof

Info

Publication number: CN115815882A
Application number: CN202211662153.3A
Authority: CN
Inventors: 王思远; 刘硕; 罗树全; 徐朴
Original assignee: Shenzhen Fitech Co ltd
Current assignee: Shenzhen Fitech Co ltd
Priority date: 2022-12-23
Filing date: 2022-12-23
Publication date: 2023-03-21
Anticipated expiration: 2042-12-23
Also published as: CN115815882B

Abstract

The soldering flux for micro-bump welding of the electronic element and the preparation method and the welding method thereof comprise, by mass, 70-90% of liquid epoxy resin, 1-10% of organic acid, 0.5-2% of surfactant and 5-20% of curing agent; the ratio of curing agent to liquid epoxy resin ranges from 5 to 20. The soldering flux is particularly suitable for MiniLED/MicroLED, SIP or 3D packaging and welding. Meanwhile, the adhesive has the functions of bonding during chip transfer, soldering assisting during chip heating and soldering, and reinforcing after chip soldering, has no volatilization and bubbles caused by volatilization, and subsequently does not need to perform the process steps of cleaning and bottom glue filling, thereby achieving multiple purposes; the method has the advantages of greatly improving the welding precision and quality and the welding reliability, simplifying the production process, saving the production cost, being more environment-friendly, having no solvent volatilization and no need of cleaning, and reducing the pollution caused by volatilization and cleaning.

Description

Solvent-free rosin-free soldering flux for micro-bump welding and preparation and soldering assisting methods thereof

Technical Field

The application relates to the technical field of microelectronic and semiconductor packaging materials, in particular to a solvent-free and rosin-free soldering flux and a preparation method and a welding method thereof.

Background

With the development of microelectronic technology, the size of packaged chips is greatly reduced. The number of chips and the pins of the chips are increased by ten times or even one hundred times as the chip size is reduced on the substrate with the same area size. The properties of the corresponding packaging and soldering materials also need to be adjusted to follow the changes in the application scenario.

The soldering flux is a chemical substance which can help and promote the soldering process in the soldering process, and has a protective effect and an oxidation reaction prevention effect. The flux includes a solid flux, a liquid flux, and a gaseous flux. The main effect lies in assisting heat conduction, removing the oxide, reducing by welding material surface tension, removing by welding material surface greasy dirt, increase welding area, prevent several aspects such as reoxidation, the more crucial effect in these several aspects is two exactly: the method comprises the steps of removing oxides and reducing the surface tension of welded materials.

In the soldering process of electronic components, the flux is usually a mixture with rosin as a main component, and is an auxiliary material for ensuring the smooth proceeding of the soldering process. The soldering is a main process in electronic assembly, the soldering flux is an auxiliary material used in soldering, the main function of the soldering flux is to remove oxides on the surfaces of solder and soldered parent metal, so that the metal surface can reach necessary cleanliness, the surface reoxidation during soldering can be prevented, the surface tension of the solder can be reduced, the soldering performance can be improved, and the quality of electronic products can be directly influenced.

In the last decades, rosin resin scaling powders mainly comprising rosin, resin, halide-containing active agents, additives and organic solvents are generally used in the soldering process of electronic product production, and although the scaling powders have good solderability and low cost, the residues after soldering are high; the residues contain halogen ions, which gradually causes the problems of electrical insulation performance reduction, short circuit and the like, and in order to solve the problems, the residues of the rosin resin scaling powder on the electronic printed board must be cleaned, so that the production cost is increased, and the cleaning agent for cleaning the residues of the rosin resin scaling powder is mainly a fluorine-chlorine compound; the compound is a loss substance of an atmospheric ozone layer, belongs to banning and being eliminated, and a technology which is still used by a plurality of companies belongs to the technology of adopting rosin resin soldering flux for soldering and then cleaning by using a cleaning agent, so that the efficiency is lower, and the cost is higher.

In the prior art, the application number is "CN201510438826.0", the invention name is "tin-based solder for packaging inverted LED chip and its preparation method", and a tin-based solder is disclosed, because it contains "low melting point tin-based solder powder mixed filler 70.0% -90.0%", it is mainly used for establishing metal connection in soldering, and it also contains rosin as a component, it needs to be cleaned by cleaning agent, and the comprehensive efficiency needs to be improved.

In the prior art, in the patent application with the application number of CN202011590000.3 and the invention name of halogen-free water-washing soldering flux, lead-free halogen-free water-washing tin paste and a preparation method thereof, the disclosed soldering flux is suitable for tin paste with common particle size and can also be prepared into ultra-micro tin paste of T5-T8 type, the soldering spot has good activity, no tin bead is scattered, the void ratio after soldering is low, and the service window period is long; the dosage of the active agent is small, the activity is strong, and the residues do not contain halogen, so that the components are not corroded, and halogen pollution to cleaning water is not caused; the water is easy to treat after cleaning, so that the environmental burden can be reduced. But the solvent content is high, the solvent content reaches 60% -78% in mass percentage, the solvent occupies a large end of the mass of the soldering flux, the solvent is very volatile in the welding process and cannot participate in the construction of welding connection strength, bubbles can be generated in the volatilization process to have adverse effects on the connection reliability of soldering welding, and the volatilized solvent can corrode and pollute production equipment.

In the prior art, the patent application with the application number of CN202110498889.0 and the invention name of 'anisotropic conductive adhesive and adhesive film and preparation method thereof', the content range of tin-based metal powder is higher than that of the prior art, organic acid active agent is added into the soldering-assistant adhesive, and the influence of the surface oxide film of the tin-based metal powder on the formation of metallurgical connection can be effectively balanced, so that the metallurgical connection effect is better. However, the flux-assisted adhesive still contains 30% -50% of solvent by mass, occupies a large part of the composition mass, and can generate air bubbles and volatilization problems caused by the solvent.

With the development of semiconductors and microelectronics, the electrical connection bumps of devices are smaller and smaller, the connection packaging points are smaller and smaller, the packaging density is higher and higher, the requirement for soldering flux is higher and higher, the extremely small solder joint spacing makes cleaning more difficult, and a small amount of bubbles may cause quality problems.

In particular, the MiniLED, micro LED technology, i.e., LED scaling and matrixing technology, which has been rapidly developed in recent years, refers to the integration of a high-density, micro-sized LED array on one chip. It is necessary to make the LED (light emitting diode) backlight thinner, smaller, and arrayed. The LED unit can be made smaller than 50 microns, only 1% of a normal LED. And, like OLEDs, can achieve individual addressing of each picture element and individual driving of light emission. The LED light source has the advantages of inheriting the characteristics of high efficiency, high brightness, high reliability, quick response time and the like of an inorganic LED, having the characteristic of self luminescence without a backlight source, being small in size, light and thin, and being capable of easily realizing the effect of energy conservation. However, such small dimensions present new technical challenges for the fabrication and packaging of minileds, micro-leds. MiniLED is an LED chip with the size of 100 μm, and the size of the MiniLED is between that of a small-pitch LED and that of a MicroLED, which is the result of further refinement of the small-pitch LED. The LED with small spacing refers to an LED backlight source or a display product with the spacing between adjacent lamp bead points below 2.5 mm.

Compared with the LCD display technology, the miniLED and the MicroLED have relatively direct display modes, simpler structures, more excellent display effects, higher response speed in magnitude order, lighter and thinner screen and greatly reduced power consumption; the display device has the advantages that excellent display effect and flexibility are maintained, and meanwhile, the response speed is higher, and the high-temperature reliability is higher; higher brightness, high dynamic range and wide color gamut can be supported to achieve fast update rate and lower power consumption.

The MiniLED can be used as a backlight source to be applied to products such as large-size display screens, smart phones, vehicle panels, electronic contest type notebooks and the like, and can also be used for realizing self-luminous display by using RGB three-color LED chips; and the micro LED possesses minimum interval, high contrast and high refresh rate, is applicable to intelligent wearing field that closely watched such as intelligent wrist-watch, AR, VR.

Gradually transition to the booth apart from the product from big interval LED, and then enter into booth apart from and the microspur market below the P2.5 interval to gradually obtain wider application in indoor demonstration field, the lamp pearl interval constantly reduces, and display effect continuously promotes. Small pitch LEDs have become the dominant growth factor for current LED displays. At present, the LED small-spacing display technology, process and industrial chain matching are mature. The cost price is continuously dropping and the wide space of indoor display has been successfully opened, but the small-pitch LED still has physical technical limitation, so the smaller-pitch Mini/micro LED starts to be reflected in the popular eye curtain. P generally represents a pixel pitch, which refers to a central distance between two adjacent beads on the led display screen, also called a dot pitch, and a value behind P mainly refers to a distance between two pixel points, which is generally called a dot pitch. For example, the distance between the p2.5led display screens is 2.5mm, the distance between the p3led display screens is 3mm, and the distance between the p4led display screens is 4mm, wherein the lower the distance density is, the more densely the lamp beads are distributed, and the more clear the display effect is. The indoor LED display screen comprises p1.0, p1.25, p1.37, p1.53, p1.667, p2, p2.5, p3, p4, p5, p6 and the like. The outdoor LED display screens p3, p4, 5, p6, p8, p10 and the like, wherein p2.5 represents that the distance between two pixels is 2.5mm, the smaller the distance value of the point is, the higher the unit pixel point is, the clearer the display picture is, but the manufacturing difficulty, particularly the welding requirement is higher.

MiniLED reduces the size of traditional LED crystal grains to 100-300 mu m, greatly improves the number of backlight sources, and realizes regional brightness adjustment by matching with corresponding control, thereby bringing better visual experience. The scheme has the characteristics of energy conservation, lightness and thinness, wide color gamut, ultrahigh contrast, fine dynamic partition and the like, can overcome the defects of other backlight modes, has higher production cost at present, and is mainly used for high-end displays.

The MiniLED and micro led mass production technology still has difficulties, and the bottleneck problems encountered in the MiniLED and micro led industrial preparation include huge transfer and electrode connection problems, namely how to transfer tens of thousands of micro led chips onto a TFT circuit substrate in batch mode, and assemble the chips according to micron-scale periods to form a high-density two-dimensional array structure, and ensure the reliability of the electrical connection and mechanical connection of small microelectrodes. Mass production requires a defect rate of less than one part per million, which presents a significant challenge to the production process and corresponding materials.

In MiniLED, microLED and 3D encapsulation, the size of a MiniLED chip is 100-300 μm, the size of the MicroLED is less than 100 μm, the size range of an electrode in the MiniLED is 30-100 μm, the size of the electrode in the MicroLED, namely a bonding pad, is lower to within 10 μm, and only one tenth of the diameter of one hair; generally, the smaller the chip size, the smaller the size of its electrodes, i.e. electrical connection contacts, and the lower the reliability of its mechanical connection; the difficulty is that the small micro-solder joint needs to ensure the reliability of the mechanical connection while ensuring the reliability of the electrical connection after soldering.

The number of pixels on a 2-square-centimeter direct display substrate reaches 131 ten thousand, each pixel relates to RGB three-color LEDs, the number of LEDs reaches 393 ten thousand, the chip size is miniaturized, the number of devices on a single PCB board is increased exponentially, the size and the thickness of holes formed in a steel mesh are limited, conventional solders have the risks of residues, tin beads, short circuits and high defect rate, and the requirements of an advanced packaging process cannot be met. How to package the LED chip and the substrate, what packaging material is selected, what process is adopted, how to transfer the package to the bonding pad, how to quickly attach the chip in place, how to improve the yield, how to reduce the cost and the like are key problems to be solved, and the development speed and the prospect of a photoelectric display enterprise are determined.

In order to solve the problems, the development of a packaging material suitable for micro-electronic and semiconductor micro-bump fine pitch high packaging density is urgently needed, and a solvent-free and rosin-free soldering aid adhesive is developed in the application, so that the technical problems of the packaging material can be effectively solved.

The noun explains:

MiniLED, the size of MiniLED by the organization of the China ultra high definition video industry alliance is defined as the chip size controlled within 300 μm. The size range of the electrodes in the MiniLED is 30 to 100 mu m, namely the size range of the micro-bumps to be welded is 30 to 100 mu m.

The size of the MicroLED is defined as the chip size controlled within 100 mu m by the MicroLED and the China ultra high definition video industry alliance organization. The size of an electrode, namely a bonding pad, in the MicroLED is further reduced to be within 10 mu m, namely the size range of a micro bump to be welded is less than 10 mu m.

The 3D package refers to a packaging technique in which two or more chips are stacked in a vertical direction in the same package without changing the size of the package.

SIP packaging (System In Package) is a packaging scheme that a plurality of functional wafers, including functional wafers such as processors and memories, are integrated into one Package according to factors such as application scenes and the number of layers of a packaging substrate, so that a basic complete function is realized.

In the application document, the particle size specification of welding alloy powder or IPCJ-STD-005A-2012 for welding electronic products in the electronic industry standard SJ/T11391-2019 is adopted; symbols T7 to T8 represent particle diameter range signals; the units are microns, i.e., μm;

the T7 type powder shows a particle diameter range in which: 2-11 μm;

the T8 type powder shows a particle diameter range in which: 2-8 μm;

the T9 type powder shows a particle diameter range in which: 1-5 μm;

the T10 type powder shows a particle diameter range in which: 1-3 μm.

Disclosure of Invention

The technical scheme of the application overcomes the defects of the prior art and creatively provides the solvent-free rosin-free soldering flux for micro bump welding and the preparation and welding method thereof, and the solvent-free rosin-free soldering flux can be suitable for welding of MiniLED/MicroLED, SIP or 3D packaging.

The solvent-free rosin-free soldering flux for micro-bump welding comprises, by mass, 70% -90% of liquid epoxy resin, 1% -10% of organic acid, 0.5% -2% of surfactant and 5% -20% of curing agent; the ratio of the curing agent to the liquid epoxy resin in percentage by mass is in the range of 5 to 20.

The liquid epoxy resin is any one or more of bisphenol A resin E51, bisphenol A resin E44, NPEL-128S, bisphenol A-DER332 and bisphenol A-DER 331.

The organic acid comprises any one or more of adipic acid, phenylsuccinic acid, itaconic acid, methylsuccinic acid, isoadipic acid, isooctanoic acid, furoic acid, tetracosanoic acid and azelaic acid.

The surfactant is any one or more of WE-3220, FS-3100 and TL-X60.

The curing agent comprises any one or more of modified amine latent curing agent HAA-1021, dicyandiamide and 594 epoxy curing agent.

The chemical crystal size in the soldering flux is less than or equal to 10 microns.

And 0-5% of thixotropic agent by mass percentage.

The thixotropic agent comprises any one or more of modified polyamide wax powder, a thixotropic agent R, a SUPER thixotropic agent, a thixotropic agent K630 and modified hydrogenated castor oil.

The technical scheme for solving the technical problems can also be a preparation method of the solvent-free rosin-free soldering flux for micro-bump welding, which is used for preparing the solvent-free rosin-free soldering flux for micro-bump welding; the method comprises the following steps of A1: sequentially adding liquid epoxy resin and organic acid into a container at the temperature of 70-90 ℃, and stirring for 30-60 minutes until the mixture is uniform and liquid, and no visible particles and liquid layering exist; step A2: cooling the uniform liquid obtained in the step A1 to 30 ℃; step A3: adding a curing agent and a surfactant into the uniform liquid at 30 ℃ obtained in the step A2, and stirring for 10-30 minutes; or step A3 is replaced by step B3 and step B4; and step B3: adding a surfactant into the uniform liquid at 30 ℃ obtained in the step A2, and stirring for 10-30 minutes; and step B4: and C, adding a curing agent and stirring for 10-30 minutes on the basis of the step B3.

The technical scheme for solving the technical problems can also be a preparation method of the solvent-free rosin-free soldering flux for micro-bump welding, which is used for preparing the solvent-free rosin-free soldering flux for micro-bump welding; the method comprises the following steps of C1: sequentially adding liquid epoxy resin and organic acid into a container at the temperature of 70-90 ℃, and stirring for 30-60 minutes until the mixture is uniform and liquid, and no visible particles and liquid layering exist; and step C2: adding a thixotropic agent and stirring for 30 minutes; and C3: cooling the uniform liquid obtained in the step C2 to 30 ℃; and C4: adding a curing agent and a surfactant into the uniform liquid obtained in the step C3, and stirring for 10-30 minutes; or step C4 is replaced by step D4 and step D5; step D4: c, adding a surfactant into the uniform liquid obtained in the step C3, and stirring for 10-30 minutes; step D5: on the basis of the step D4, adding a curing agent and stirring for 10-30 minutes; and C6: and D, grinding the soldering flux obtained in the step C4 or the step D5 by a three-roll grinder or a ball mill to obtain the solvent-free rosin-free soldering flux.

The technical scheme for solving the technical problem can also be a welding assisting method which is used for micro-bump welding; the size range of the micro-bumps is 1-500 mu m; the solvent-free rosin-free soldering flux for micro-bump soldering is based on the above.

And (3) welding processes for MiniLED, microLED, SIP or 3D packaging.

The welding assisting method comprises the following steps of E1: coating the solvent-free rosin-free soldering flux around the micro-convex points to be welded; the thickness of the solvent-free rosin-free soldering flux is 50% -100% of the height of the micro convex point to be welded; step E2: applying energy at and around the to-be-welded micro-convex points to complete the brazing process of the to-be-welded micro-convex points and the to-be-welded surface, wherein the solvent-free and rosin-free soldering flux is melted and uniformly distributed around the micro-convex points in the brazing process.

The technical scheme for solving the technical problems can also be a high-speed crystal-pricking process method under the condition of mass transfer of the MiniLED/MicroLED, and is based on the solvent-free rosin-free soldering flux for micro bump welding. Comprising the following steps of F1: pre-plating solder on the MiniLED/micro LED chip, and then transferring the chip to a carrier blue film; step F2: coating the solvent-free rosin-free soldering flux for micro bump welding on the LED substrate; step F3: aligning the carrier blue film in the step F1 to an LED substrate, wherein the LED substrate is made of FR4 or glass substrate, a space of 0.010mm-2.0 mm is reserved between the blue film and the LED substrate, and a MiniLED/microLED chip on the carrier blue film is peeled off under the action of laser, so that the MiniLED/microLED chip quickly falls on a pad of the LED substrate coated with the solvent-free and rosin-free soldering flux, the solvent-free and rosin-free soldering flux fixes the chip, or the chip is adhered to the pad by using a needle-punching mechanical force; step F4: the LED substrate completely completes a laser transfer type or crystal-piercing transfer process, then the chip and the substrate are metallurgically connected through a solvent-free and rosin-free scaling powder in a heating mode, the electric conduction and heat conduction functions are realized, meanwhile, the solvent-free and rosin-free scaling powder residues are filled in gaps and the periphery of welding spots, solidification is completed, and the bonding and electric protection effects are realized.

Compare with prior art, one of the beneficial effect of this application is: the solvent-free rosin-free soldering flux for micro-bump welding does not contain any solvent in the formula, and is safe and environment-friendly, and no solvent volatilizes after curing, and no Voc volatilizes.

Compare with prior art, another one of the beneficial effect of this application: the method overcomes the problem that the conventional soldering flux, soldering paste or soldering paste contains solvent which volatilizes to cause the generation of bubble cavities, reduces the void ratio in welding and the volume of bubbles in a cured substance, and improves the welding reliability.

Compare with prior art, the beneficial effect of this application is three: the curing shrinkage rate is low, because the curing of the epoxy resin mainly depends on the ring-opening addition polymerization of epoxy groups, no low molecular substance is generated in the curing process, the epoxy resin has secondary hydroxyl groups, the molecules are tightly arranged due to the association of the secondary hydroxyl groups and the hydrogen bonds of the epoxy resin, the curing shrinkage rate is generally within 2 percent, the internal stress of the epoxy resin is small, the epoxy resin is not easy to crack, and the micro-convex points or BGA balls on a device or a carrier plate can be effectively and metallurgically connected with and supplemented to a bonding pad.

Compare with prior art, the beneficial effect of this application is four: the solid content is high, the welding curing volatilization rate is low, the maximum protection function is realized by the minimum application amount, a cured substance is protected around a welding spot to the maximum extent, the high resin amount improves the bonding strength of the solidified soldering flux, the fine space is perfectly filled, the protection performance is enhanced, the electric insulation between pins or micro-bumps is ensured, the mechanical connection characteristic between a device and a substrate is also enhanced, the mechanical connection characteristic between the device and the substrate is obviously enhanced, not only is the mechanical connection characteristic between the micro-bumps and the substrate enhanced, but also the mechanical connection characteristic between the whole chip and the substrate is enhanced, and the connection reliability of the micro-bumps or the micro-electrodes in the micro-device is greatly improved.

Compare with prior art, the beneficial effect of this application is five: before welding energy is applied, the formula contains a large amount of liquid epoxy resin, so that the adhesive force is high, the adhesive force is very suitable for a Mini/MicroLED high-speed mass transfer process, the adhesive force to a chip in a high-speed transfer process can be ensured, the chip can be fixed and adsorbed in time after being transferred, the probability of position deviation is reduced, the realization of welding size precision is ensured, and the yield of chip packaging is improved.

Compare with prior art, the beneficial effect of this application is six: the adhesive does not contain rosin resin, has higher bonding strength after curing, does not need to be cleaned after curing, reduces the process links, saves the process cost, and is more environment-friendly and energy-saving.

Compare with prior art, seven of the beneficial effect of this application are: the content of the organic acid is suitable, the method is very suitable for the welding assistance of the microelectrode or the micro bump in the Mini/MicroLED high-speed mass transfer process, and an oxide layer on the microelectrode or the micro bump can be quickly removed, so that the metal melting and connecting processes in the brazing process are smoother.

Compare with prior art, eight of the beneficial effect of this application are: the content of the surfactant is proper, the surface tension of the soldering flux and the preset solder in a molten state can be reduced, the soldering flux and the preset solder can quickly wet the bonding pad, and the soldering flux is very suitable for the soldering assistance of microelectrodes or micro-bumps, so that the metal melting and connecting processes in soldering are smoother.

Compare with prior art, nine of this application's beneficial effect are: meanwhile, the soldering flux has the functions of bonding during chip transfer, soldering aid during chip heating and soldering, and reinforcement after chip soldering, has no bubbles caused by voc volatilization and solvent volatilization, and is not required to be subjected to the subsequent process steps of cleaning and bottom glue filling, thereby achieving multiple purposes, being an inexhaustible comprehensive soldering flux, greatly improving the precision quality and the soldering reliability of soldering, simplifying the production process, saving the production cost, being more environment-friendly, having no solvent volatilization and no need of cleaning, and reducing the pollution caused by volatilization and cleaning.

Drawings

FIG. 1 is a table of formulation components for a solvent-free, rosin-free flux for micro-bump welding; the tables list the formulations of 10 examples and 3 comparative examples;

FIG. 2 is a table of further refinements of the 10 example formulations and the 3 comparative formulations of FIG. 1;

FIG. 3 is a table comparing test data for 10 example formulations and 3 comparative examples referred to in FIG. 2 after welding tests under equivalent conditions;

FIG. 4 is a listing of CAS NO numbers for some of the materials referred to in this application;

FIG. 5 is a list of manufacturers of the partial materials referred to in this application;

FIG. 6 is a schematic diagram of a prior art flux or flux participating in a soldering process; it can be seen from the figure that the flux before and after welding is only distributed in a small range around the welding point, a large gap exists between the welding point and the welding point, welding residual substances are easy to remain in the gap, and the bonding force between the chip and the welding surface is only limited to the metallurgical connection between the welding points and the bonding force of the flux around the welding point;

FIG. 7 is a schematic illustration of the participation of the flux in the soldering process of the present application; as can be seen from the figure, the epoxy curing glue in the soldering flux is not only distributed in a small range around the soldering point before and after soldering, but also fills the soldering point and the gap before the soldering point, so that no soldering residual substance exists between the soldering point and the gap between the soldering point, and the adhesive force between the chip and the soldering surface is greatly enhanced;

fig. 8 is a cross-sectional view of a solder joint after soldering using the flux and fluxing method of the present application.

Detailed Description

The present disclosure is described in further detail below with reference to the drawings.

The purpose of the application is to solve the problems that poor welding is caused by solvent volatilization in the Mini/micro LED welding process, for example, chip displacement is caused by bubble breakage, the packaging efficiency is reduced due to the complexity of the packaging process, for example, rosin resin residue needs to be cured and reinforced by filling colloid after solvent cleaning, and the process is not only complicated, but also greatly reduces the packaging efficiency and yield.

Wt% in the present document means mass percent. rpm is the unit of rotational speed, meaning revolutions per minute, min is the unit of time minutes. In this document, the CAS No for some of the substance names involved is shown in the Table of FIG. 4; CAS No is a registration number ordered for chemicals by the american Chemical Abstracts Service (CAS). Some other manufacturers of materials referred to in this application without a CAS No. are shown in the table in fig. 5.

As shown in fig. 1 and fig. 2, an embodiment of a solvent-free rosin-free flux for micro-bump welding comprises, by mass, 70% to 90% of a liquid epoxy resin, 1% to 10% of an organic acid, 0.5% to 2% of a surfactant, and 5% to 20% of a curing agent; the ratio of curing agent to liquid epoxy resin ranges from 5 to 20.

FIG. 1 is a table of formulation components for a solvent-free, rosin-free flux for micro-bump welding; the tables list the formulations of 10 examples and 3 comparative examples; FIG. 2 is a table of further refinements of the 10 example formulations and the 3 comparative formulations of FIG. 1.

The liquid epoxy resin is any one or more of bisphenol A resin E51, bisphenol A resin E44, NPEL-128S, bisphenol A-DER332 and bisphenol A-DER 331. The organic acid comprises any one or more of adipic acid, phenylsuccinic acid, itaconic acid, methylsuccinic acid, isoadipic acid, isooctanoic acid, furoic acid, tetracosanoic acid and azelaic acid. The surfactant is any one or more of WE-3220, FS-3100 and TL-X60. The curing agent comprises any one or more of modified amine latent curing agent HAA-1021, dicyandiamide and 594 epoxy curing agent. The chemical crystal size in the soldering flux is less than or equal to 10 microns.

The solvent-free rosin-free soldering flux for micro-bump welding comprises, by mass, 70% -90% of liquid epoxy resin, 1% -10% of organic acid, 0.5% -2% of surfactant and 5% -20% of curing agent; the ratio of curing agent to liquid epoxy resin ranges from 5 to 20. And 0-5% of thixotropic agent by mass percentage. The thixotropic agent comprises any one or more of modified polyamide wax powder, a thixotropic agent R, a SUPER thixotropic agent, a thixotropic agent K630 and modified hydrogenated castor oil.

Specific examples 1 to 10, and corresponding comparative examples 1 to 3, are shown in table 3.

In a specific example 1 of the solvent-free and rosin-free flux, the flux comprises, by mass, 80 parts of epoxy resin bisphenol A-DER332, 7 parts of bisphenol A-DER331, 3 parts of adipic acid, 3 parts of phenylbutanedioic acid, 1 part of modified hydrogenated castor oil, 1 part of surfactant WE-3220, 3 parts of curing agent HAA-1021, and 2 parts of curing agent 594. The adhesive comprises 87 mass percent of liquid epoxy resin, 5 mass percent of curing agent, 1 mass percent of surfactant, 1 mass percent of thixotropic agent and 6 mass percent of organic acid; wherein 87% of the liquid epoxy resin comprises 80% of epoxy resin bisphenol A-DER332 and 7% of bisphenol A-DER 331; 6% of organic acid comprises 3% of adipic acid and 3% of phenyl succinic acid; 1% of thixotropic agent is modified hydrogenated castor oil 1%; the surfactant WE-3220 is 1%; 5% of curing agent is 3% of curing agent HAA-1021, and 2% of curing agent 594.

In a specific solvent-free and rosin-free flux example 2, the flux comprises 78% of liquid epoxy resin, 15% of curing agent, 2% of surfactant and 5% of organic acid by mass percent; wherein the liquid epoxy resin comprises 30 percent of NPEL-128S and 48 percent of bisphenol A-DER 332; 5% of organic acid comprises 1% of phenyl succinic acid and 4% of isooctyl acid; 2% of surfactant is WE-3220; 15% of curing agent is curing agent HAA-1021.

In a specific solvent-free and rosin-free flux example 3, the flux comprises, by mass, 85% of a liquid epoxy resin, 10% of a curing agent, 0.5% of a surfactant, 1.5% of a thixotropic agent and 3% of an organic acid; wherein the liquid epoxy resin comprises 45% of bisphenol A-DER332 and 40% of bisphenol A-DER 331; 3% of organic acid comprises 1% of adipic acid and 2% of phenylsuccinic acid; 1.5 percent of thixotropic agent is modified polyamide wax powder; 10% of curing agent comprises 8% of curing agent HAA-1021 and 2% of 594 epoxy curing agent; 0.5% of surfactant is FS-3100.

In a specific solvent-free and rosin-free flux example 4, the flux comprises, by mass, 82% of a liquid epoxy resin, 7% of a curing agent, 1% of a surfactant, 5% of a thixotropic agent and 5% of an organic acid; wherein the liquid epoxy resin comprises 50% of bisphenol A type resin E44 and 32% of bisphenol A-DER 331; 5% of organic acid comprises 3% of azelaic acid and 2% of tetracosanoic acid; 5% of thixotropic agent is modified polyamide wax powder; 7% of curing agent comprises 3% of curing agent HAA-1021 and 4% of 594 epoxy curing agent; 0.5% of the surfactant 1% is FS-3100, and 0.5% is WE-3220.

In a specific solvent-free and rosin-free flux example 5, the flux comprises 89% of liquid epoxy resin, 9% of curing agent, 1% of surfactant and 1% of organic acid by mass percent; wherein the liquid epoxy resin comprises 59% of bisphenol A resin E44 and 30% of bisphenol A-DER 331; 1% of organic acid comprises 1% of adipic acid; 9% of curing agent comprises 4% of curing agent HAA-1021 and 5% of 594 epoxy curing agent; the surfactant 1% is WE-3220.

In a specific solvent-free and rosin-free flux example 6, the flux comprises, by mass, 85% of a liquid epoxy resin, 5% of a curing agent, 1% of a surfactant, 3% of a thixotropic agent and 6% of an organic acid; wherein the liquid epoxy resin comprises 5% of bisphenol A type resin E51 and 80% of bisphenol A-DER 332; 6% of organic acid comprises 3% of methylsuccinic acid and 3% of itaconic acid; the thixotropic agent 3% comprises 2% of thixotropic agent R and 1% of modified hydrogenated castor oil; 5% of curing agent comprises 3% of curing agent HAA-1021 and 2% of 594 epoxy curing agent; the surfactant 1% is WE-3220.

In a specific solvent-free and rosin-free flux of example 7, the flux comprises, by mass, 78% of a liquid epoxy resin, 10% of a curing agent, 2% of a surfactant and 10% of an organic acid; wherein the liquid epoxy resin comprises 30 percent of bisphenol A type resin E44, 28 percent of bisphenol A-DER332 and 20 percent of NPEL-128S; 10% of organic acid comprises 4% of adipic acid, 3% of phenyl succinic acid, 1% of isooctyl acid and 2% of furoic acid; 10% of curing agent comprises 10% of curing agent HAA-1021; the surfactant 2% is WE-3220.

In a specific solvent-free and rosin-free flux example 8, the flux comprises, by mass, 85% of a liquid epoxy resin, 10% of a curing agent, 1% of a surfactant, 1% of a thixotropic agent, and 3% of an organic acid; wherein the liquid epoxy resin comprises 45 percent of NPEL-128S and 40 percent of bisphenol A-DER 331; 3% of organic acid comprises 1% of adipic acid and 2% of phenyl succinic acid; 1% of thixotropic agent is SUPER thixotropic agent; 10% of curing agent comprises 8% of curing agent HAA-1021 and 2% of 594 epoxy curing agent; the surfactant 1% is FS-3100.

In a specific solvent-free and rosin-free flux of example 9, the flux comprises, by mass, 70% of a liquid epoxy resin, 20% of a curing agent, 0.5% of a surfactant, 1% of a thixotropic agent, and 8.5% of an organic acid; wherein the liquid epoxy resin comprises 50% of NPEL-128S and 20% of bisphenol A-DER 331; 8.5 percent of organic acid comprises 3 percent of phenyl succinic acid, 1.5 percent of isooctyl acid, 3 percent of isoadipic acid and 1 percent of arbitrarily-mixed diacid; 1% of thixotropic agent is modified polyamide wax powder; 20% of curing agent comprises 16% of curing agent HAA-1021 and 4% of 594 epoxy curing agent; the surfactant 0.5% is WE-3220.

In a specific solvent-free and rosin-free flux example 10, the flux comprises, by mass, 90% of a liquid epoxy resin, 8% of a curing agent, 1% of a surfactant and 1% of an organic acid; wherein the liquid epoxy resin comprises 5% of NPEL-128 and 85% of NPEL-128S; 1% of organic acid comprises 1% of adipic acid; 8 percent of curing agent is curing agent HAA-1021; the surfactant 1% is WE-3220.

The preparation method of the solvent-free and rosin-free flux in the

above embodiments

2, 5, 7, and 10 includes the following steps: step A1: sequentially adding liquid epoxy resin and organic acid into a container, heating to 85 ℃, stirring at 1000rpm for 30 minutes until the epoxy resin is uniform and liquid, namely, no visible particles and no liquid layering exist; step A2: cooling the uniform liquid obtained in the step A1 to 30 ℃; step A3: and C, adding the curing agent and the surfactant into the uniform liquid at the temperature of 30 ℃ obtained in the step A2, and stirring for 20 minutes.

The preparation method for obtaining the solvent-free and rosin-free scaling powder by replacing the step A3 with the step B3 and the step B4 comprises the following steps: step A1: sequentially adding liquid epoxy resin and organic acid into a container, heating to 85 ℃, stirring at 1000rpm for 30 minutes until the epoxy resin is uniform and liquid, namely, no visible particles and no liquid layering exist; step A2: cooling the uniform liquid obtained in the step A1 to 30 ℃; and step B3: adding a surfactant into the uniform liquid at 30 ℃ obtained in the step A2, and stirring for 15 minutes; and step B4: and C, on the basis of the step B3, adding a curing agent and stirring for 15 minutes to obtain the solvent-free rosin-free scaling powder. In some embodiments, when the powder-like substance is not present in the added components, the solvent-free rosin-free flux can be obtained by the step B4. In other embodiments, when the powdered substance is present in the added components, after step B4, step B5 is further included: and B2, grinding the soldering flux obtained in the step A2 or the step B4 by a three-roll grinder or a ball mill to obtain the solvent-free rosin-free soldering flux.

The preparation method of the solvent-free and rosin-free flux in the

above embodiments

1, 3, 4, 6, 8, and 9 includes the following steps: step C1: sequentially adding liquid epoxy resin and organic acid into a container at the temperature of 70-90 ℃, and stirring for 30-60 minutes until the mixture is uniform and liquid, and no visible particles and liquid layering exist; and step C2: adding a thixotropic agent and stirring for 30 minutes; and C3: cooling the uniform liquid obtained in the step C2 to 30 ℃; and C4: adding a curing agent and a surfactant into the uniform liquid obtained in the step C3, and stirring for 10-30 minutes; or step C4 is replaced by step D4 and step D5; and D4: c, adding a surfactant into the uniform liquid obtained in the step C3, and stirring for 10-30 minutes; step D5: on the basis of the step D4, adding a curing agent and stirring for 10-30 minutes; step C6: and D, grinding the soldering flux obtained in the step C4 or the step D5 by using a three-roll grinder or a ball mill to obtain the solvent-free and rosin-free soldering flux.

FIG. 3 is a table comparing test data for 10 example formulations and 3 comparative examples referred to in FIG. 2 after welding tests under equivalent conditions. Comparative examples 1 to 3 are conventional fluxes prepared according to the formulations in the table of fig. 2. As can be seen from the test result data of FIG. 3, the resistance thrust after welding of examples 1 to 10 is above 40N, which is far beyond the level of comparative examples 1 to 3. After welding the solvent-free and rosin-free type flux obtained in the examples 1 to 10 and the comparative examples 1 to 3, carrying out performance test; and (3) viscosity testing: testing the viscosity of each sample by adopting a MalcomPCU02V rotational viscometer, wherein the rotating speed of testing parameters is 10rpm, and the temperature is 25 ℃; adhesion force: the adhesion force of each sample is tested by adopting a MalcomTK-1 adhesion force testing device and a JISZ3284b standard, so that the die bonding capability at a high speed is ensured, and the testing parameters are as follows: the sample was printed at a thickness of 0.2mm, a print diameter of 6.5mm, a test probe diameter of 5.1mm, a dipping speed of 2.0mm/s, a punching force of 50g, a punching time of 0.2s, and a pull-off speed of 10mm/s. Residual solid content of the soldering flux: the residual solid content of each sample was tested using a relaxation-resistant TG209F3 thermogravimetric analyzer. Testing parameters: the temperature rise range is 30 to 300 ℃, the temperature rise rate is 30 ℃/min, and the inert gas is high-purity argon gas at a rate of 20ml/min. Shear thrust of the resistance device: and (3) pasting 0603 resistors on the printed samples, completing welding and curing according to curing temperature time, and testing resistance thrust after welding.

From the test results, the curing time of the solvent-free and rosin-free soldering flux disclosed by the invention is under the thermal reflux process condition of @ 150 ℃ for 5min or @ 180 ℃ for 3min or @ 240 ℃ for 2min, the adhesive force is more than 200g, and the resistance thrust is more than 40N after connection, so that the requirement of the commercial rosin-free and solvent-free soldering flux is met.

FIG. 7 is a schematic diagram illustrating a fluxing method for micro bump soldering using a solventless, rosin-free flux of the present application; the size range of the micro-bumps is 1-500 mu m; the soldering assisting method is used for the soldering process of MiniLED, microLED, SIP or 3D packaging. The welding assisting method comprises the following steps of E1: coating the solvent-free rosin-free soldering flux around the micro-convex points to be welded; the thickness of the solvent-free rosin-free soldering flux is 50% -100% of the height of the micro convex point to be welded; and E2: applying energy to the micro-convex points to be welded and the periphery of the micro-convex points to be welded to enable the micro-convex points to be welded and the surface to be welded to finish the brazing process, wherein the epoxy curing glue in the solvent-free rosin-free soldering flux is melted and uniformly distributed around the micro-convex points in the welding process. For enhancing the adhesion of the microbumps to their bonding surfaces and for providing insulation between the microbumps. As can be seen from fig. 7, the epoxy curing glue in the flux is not only distributed in a small range around the solder joint before and after soldering, but also fills the solder joint and the gap before the solder joint, so that no soldering residue exists between the solder joint and the bonding force between the chip and the soldering surface is greatly enhanced. FIG. 6 is a schematic diagram of a soldering flux or flux participating in a soldering process in the prior art; as can be seen from fig. 6, the fluxing adhesive before and after soldering is only distributed in a small range around the soldering point, a large gap is still formed between the soldering point and the soldering point, soldering residues are easy to remain in the gap, and the adhesive force between the chip and the soldering surface is limited to the metallurgical connection between the soldering points and the adhesive force of the fluxing adhesive around the soldering point.

FIG. 8 is a schematic cross-sectional view of a welded joint welded by the above-mentioned fluxing method, wherein B is a metallurgical joint of the welded joint, i.e., a micro bump; epoxy curing glue is filled between the metallurgical connecting points, as indicated by arrows in the figure; the epoxy curing glue is a substance which is remained around the welding spot in the welding process of the solvent-free rosin-free soldering flux.

In some embodiments of a high speed bumping process under MiniLED/micro led bulk transfer not shown in the drawings, the solvent-free rosin-free flux for micro bump bonding is based on the above. The method comprises the following steps of F1: pre-plating solder on a MiniLED/microLED chip, and then transferring the chip to a carrier blue film; step F2: coating the solvent-free rosin-free soldering flux for micro bump welding on the LED substrate; step F3: aligning the carrier blue film in the step F1 to an LED substrate, wherein the LED substrate is made of FR4 or glass substrate, a space of 0.010mm-2.0 mm is reserved between the blue film and the LED substrate, and a MiniLED/microLED chip on the carrier blue film is peeled off under the action of laser, so that the MiniLED/microLED chip quickly falls on a pad of the LED substrate coated with the solvent-free and rosin-free soldering flux, the solvent-free and rosin-free soldering flux fixes the chip, or the chip is adhered to the pad by using a needle-punching mechanical force; step F4: the LED substrate completely completes a laser transfer type or crystal-piercing transfer process, then the chip and the substrate are metallurgically connected through a solvent-free and rosin-free scaling powder in a heating mode, the electric conduction and heat conduction functions are realized, meanwhile, the solvent-free and rosin-free scaling powder residues are filled in gaps and the periphery of welding spots, solidification is completed, and the bonding and electric protection effects are realized.

As used herein, the term "consisting of 8230; preparation" is synonymous with "including". As used herein, the terms "comprises," "comprising," "has," "having," "contains," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus. The conjunction "consisting of 8230excluding any unspecified elements, steps or components.

If used in a claim, the phrase will render the claim closed except for the materials described, except for the conventional impurities associated therewith. When the phrase "consisting of 8230title" appears in a clause of the subject matter of the claims and not immediately after the subject matter, it defines only the elements described in the clause; other elements are not excluded from the claims as a whole. When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2 and 4 to 5", "1 to 3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range. The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. "optional" or "any" means that the subsequently described event or events may or may not occur, and that the description includes instances where the event occurs and instances where it does not. Approximating language, as used herein in the specification and claims, is intended to modify a quantity, such that the invention is not limited to the specific quantity, but includes portions that are literally received by modifying or otherwise modifying such quantity without substantially changing the basic function to which it is related. Accordingly, the use of "about," "about," etc. to modify a numerical value means that the invention is not limited to the precise value. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. In the present description and claims, range limitations may be combined and/or interchanged, including all sub-ranges contained therein if not otherwise stated. In addition, the indefinite articles "a" and "an" preceding an element or component of the invention are not intended to limit the number requirement (i.e., the number of occurrences) of the element or component. Thus, "a" or "an" should be read to include one or at least one, and the singular form of an element or component also includes the plural unless the stated number clearly indicates that the singular form is intended.

The above description is only an example of the present application and is not intended to limit the scope of the present application, and all modifications of equivalent structures and equivalent processes, which are made by the contents of the specification and the drawings, or which are directly or indirectly applied to other related technical fields, are intended to be included within the scope of the present application.

Claims

1. A solvent-free rosin-free soldering flux for micro-bump welding is characterized in that,

the epoxy resin curing agent comprises, by mass, 70-90% of liquid epoxy resin, 1-10% of organic acid, 0.5-2% of surfactant and 5-20% of curing agent;

the ratio of the curing agent to the liquid epoxy resin in percentage by mass is in the range of 5 to 20.

2. The solvent-free, rosin-free flux for micro-bump welding according to claim 1,

3. The solvent-free, rosin-free flux for micro-bump welding according to claim 1,

4. The solvent-free, rosin-free flux for micro-bump welding according to claim 1,

the surfactant is any one or more of WE-3220, FS-3100 and TL-X60.

5. The solvent-free, rosin-free flux for micro-bump soldering of claim 1,

6. The solvent-free, rosin-free flux for micro-bump welding according to claim 1,

7. The solvent-free, rosin-free flux for micro-bump welding according to claim 1,

and 0-5% of thixotropic agent by mass percentage.

8. The solvent-free, rosin-free flux for micro-bump welding according to claim 7,

9. A preparation method of a solvent-free rosin-free soldering flux for micro-bump welding is characterized in that,

a solvent-free, rosin-free flux for use in the preparation of a microbump soldering flux as claimed in any one of claims 1 to 6;

comprises the following steps of (a) carrying out,

step A1: sequentially adding liquid epoxy resin and organic acid into a container at the temperature of 70-90 ℃, and stirring for 30-60 minutes until the mixture is uniform and liquid, and no visible particles and liquid layering exist;

step A2: cooling the uniform liquid obtained in the step A1 to 30 ℃;

step A3: adding a curing agent and a surfactant into the uniform liquid at 30 ℃ obtained in the step A2, and stirring for 10-30 minutes;

or step A3 is replaced by step B3 and step B4;

and step B3: adding a surfactant into the uniform liquid at 30 ℃ obtained in the step A2, and stirring for 10-30 minutes;

and step B4: and C, adding a curing agent and stirring for 10-30 minutes on the basis of the step B3.

10. A preparation method of solvent-free rosin-free soldering flux for micro-bump welding is characterized in that,

a solvent-free, rosin-free flux for use in the preparation of a microbump soldering flux as claimed in any one of claims 7 to 8;

comprises the following steps of (a) carrying out,

step C1: sequentially adding liquid epoxy resin and organic acid into a container at the temperature of 70-90 ℃, and stirring for 30-60 minutes until the mixture is uniform and liquid, and no visible particles and liquid layering exist;

and step C2: adding a thixotropic agent and stirring for 30 minutes;

and C3: cooling the uniform liquid obtained in the step C2 to 30 ℃;

and C4: adding a curing agent and a surfactant into the uniform liquid obtained in the step C3, and stirring for 10-30 minutes;

or step C4 is replaced by step D4 and step D5;

and D4: c, adding a surfactant into the uniform liquid obtained in the step C3, and stirring for 10-30 minutes;

step D5: on the basis of the step D4, adding a curing agent and stirring for 10-30 minutes;

and C6: and D, grinding the soldering flux obtained in the step C4 or the step D5 by a three-roll grinder or a ball mill to obtain the solvent-free rosin-free soldering flux.

11. A welding-assistant method is characterized in that,

the method is used for micro-bump welding; the size range of the micro-bumps is 1-500 mu m;

the solvent-free and rosin-free flux for micro-bump soldering according to any one of claims 1 to 8.

12. The fluxing method of claim 11,

soldering process for MiniLED, micro led, SIP or 3D packages.

13. The fluxing method of claim 11,

comprising the steps of E1: coating the solvent-free rosin-free soldering flux around the micro-convex points to be welded; the thickness of the solvent-free rosin-free soldering flux is 50% -100% of the height of the micro convex point to be welded;

step E2: applying energy at the micro-convex points to be welded and the periphery of the micro-convex points to be welded to enable the micro-convex points to be welded and the surface to be welded to complete the brazing process, wherein the solvent-free rosin-free soldering flux is melted and uniformly distributed around the micro-convex points in the welding process.

14. A high-speed crystal-forming process under the condition of mass transfer of MiniLED/MicroLED is characterized in that,

15. The method for high-speed crystal-growth under bulk transfer of MiniLED/MicroLED according to claim 14,

comprising the following steps of F1: pre-plating solder on the MiniLED/micro LED chip, and then transferring the chip to a carrier blue film;

step F2: coating the solvent-free rosin-free soldering flux for micro bump welding on the LED substrate;

step F3: aligning the carrier blue film in the step F1 to an LED substrate, wherein the LED substrate is made of FR4 or glass substrate, a space of 0.010mm-2.0 mm is reserved between the blue film and the LED substrate, and a MiniLED/microLED chip on the carrier blue film is peeled off under the action of laser, so that the MiniLED/microLED chip quickly falls on a pad of the LED substrate coated with the solvent-free and rosin-free soldering flux, the solvent-free and rosin-free soldering flux fixes the chip, or the chip is adhered to the pad by using a needle-punching mechanical force;

step F4: the LED substrate completely completes a laser transfer type or crystal-piercing transfer process, then the chip and the substrate are metallurgically connected through a solvent-free and rosin-free scaling powder in a heating mode, the electric conduction and heat conduction functions are realized, meanwhile, the solvent-free and rosin-free scaling powder residues are filled in gaps and the periphery of welding spots, solidification is completed, and the bonding and electric protection effects are realized.